Such sanitary products as mentioned above are required to have an ability to absorb liquid excretions from human bodies and besides to have a leakproofness, breathability, comfortable properties in use and easiness of disposal after use. In general, commercially available sanitary products have a multi-layer structure of three or more layers since it is difficult to meet all of the above requirements with a single material. More precisely, as the main constituent elements of commercially available sanitary products, there are following three layers: a covering material layer which is to directly contact with human body, an absorbent material layer which is between the former layer and a liquid excretion-leakproof material layer and serves to absorb and retain therein liquid excretions, and the above mentioned liquid excretion-leakproof material layer.
The absorbent material to be used in sanitary articles must have a great capacity of water absorption and for this reason cellulosic materials such as paper, cotton and pulp have hitherto been used as the absorbent. However, materials of a great absorption capacity generally exhibit a high speed of water absorption. Therefore, if liquid excretions pass through the covering layer and contact the absorbent layer, the latter will rapidly absorb the excretions. The absorption tends to take place very locally with the result that the liquid excretions are usually difficult to be evenly permeated and distributed into the other portions of the absorbent material. The absorbent layer swelled by the local absorption of a large amount of liquid expells the liquid at a time when the external pressure applied thereto changes. This may lead to leakage of the liquid from the sanitary products. The leakage problem may be obviated if the liquid is evenly distributed throughout the absorbent material, however in general the material having a high speed of water absorption is inclined to locally absorb the liquid, which may often give rise to the leakage problem. If the leakproof layer is reinforced to prevent the leakage, the liquid evacuated from the absorbent layer will exude towards human bodies. This phenomenon is so-called "back-permeation" (or "reflux"). The phenomenon inevitably has the greatest influence on comfortableness in use of the product concerned.
In order to solve the above-mentioned problem on sanitary products, attempts have been made to distribute the liquid throughout the absorbent material by using a denser material, for example, paper or pulp fluff, employing a multi-layer structure of several kinds of materials or incorporating a material of a slow permeation speed into the absorbent layer. In general, however, a material of a lower permeation speed has a smaller water absorption, and a denser material is less flexible and increases a whole thickness or loading of the absorbent layer, which is disadvantageous in cost and comfortableness during use.
We have closely studies to avoid the drawbacks of the known products as stated above and discovered the unknown characteristics of cellulose acetate fibers. By taking advantage of the characteristics we have now succeeded in making sanitary products which have improved functions and feelings in use over the conventional products.
An object of this invention is to provide an absorbent material comprising cellulose acetate fibers and being used to make sanitary products.
Another object of the invention is to provide sanitary products, for example, disposable diapers and sanitary napkins, comprising the absorbent material.
Other objects and advantages of the invention will become apparent from the following descriptions.